1. Field of the Invention
This invention relates to a method for generating synthesized cross-sectional images, and more particularly to a method for generating such images perpendicular to a line or curve that approximates the shape of a structure scanned by a non-intrusive crosssectional image generating device.
2. Related Art
In a number of fields, including the field of medicine, computer-assisted tomography (CT), magnetic resonance (MR), and ultrasonic scanners have been employed to generate images of the interior of objects in great detail but in a non-intrusive manner. For example, a CT scanner consists of an x-ray machine and a computer. The scanner takes x-rays in thin two-dimensional cross-sectional "slices". Digitized data representing each "slice" is recorded by the computer and can be displayed on a graphics screen. One such scanner is the General Electric Model 9800 CT Scanner. A CT examination usually consists of a series of these cross-sectional views, each slice adjacent to the next (similar to slices from a loaf of bread). Similar slices can be taken by MR or ultrasonic scanning.
Such scans have been particularly useful in the medical field, where digitized scan data has been reformatted to provide synthesized images of the scanned structure in a plane or along a curve different from the plane of the original scanned images.
For example, the reformation of digitized data from such scans has in the past been used to recast data from an axial CT scan of a spine. After reformation, a synthesized image of the spine can be viewed from the sagittal or coronal planes of the body, thus providing an internal cross-sectional "slice" oriented as a "front view" or a "side view" x-ray of the spine.
It is desirable to obtain reformed images of scans of other structures in the body, such as the mandible or maxilla. As described in the co-pending patent application entitled "Method for Representing Digitized Image Data" (Ser. No. 192,586), scanned image data from such structures can be modeled by the generation of an initial curve that approximates the curvature of the scanned structure. The initial curve can be generated in a number of ways, including selection by a user of numerous data points connected by straight line segments. Another method of generating the initial curve using a cubic spline algorithm is taught in the cited co-pending application.
It is believed that the prior art has taught the reformation of scan data only along such curves or lines that conform to the shape of the scanned structure, where the curve or line itself is used to select data from the scan images. However, it has been found desirable to generate synthesized cross-sectional images perpendicular to such a line or curve. For example, it is desirable to generate cross-sectional images of a highly curved scanned structure at points perpendicular to the local curvature of the structure. Previously, it was impossible to obtain exact cross-sectional images through the desired locations in such a highly curved structure. For example, when scanning the human jaw, only axial cross-sectional scan images perpendicular to the long axis of the body can be obtained with ease. Coronal or frontal CT or MR scans can be performed by tilting a patient's head and the scanner's gantry to produce scans nearly perpendicular to the axis of the jaw bone. Such views approximate the desired cross-sectional information, but are difficult to perform (especially in the older edentulous patient population). Such views are also lacking in that they are not true cross-sections along the curvature of the scanned structure. They are only estimates of true cross-sections distorted due to the curvature of the structure.
Thus, it is desirable to obtain cross-sectional synthesized images based upon lines or curves that are derived from a line or curve conforming to the curvature of a structure.
Further, it is desirable to obtain cross-sectional synthesized images of scanned highly curved structures, with such cross-sections being truly perpendicular to the local curvature of the scanned structure.
It is therefore an object of this invention to provide a means for generating such perpendicular synthesized cross-sectional images.